JPS607547B2 - How to paint aluminum products - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for coating aluminum products.

More particularly, the present invention relates to a method of painting an aluminum product that has been anodized and has a surface structure that is in an active state. Conventionally, aluminum products are generally anodized in an electrolytic solution such as sulfuric acid, Hakama acid, or chromic acid for the purpose of imparting corrosion resistance. As a result, the oxide film formed on the surface of the aluminum product consists of a multilayer L-type y-M203 layer with countless micropores with a diameter of about 100 to 500 A.
This method alone does not provide sufficient corrosion resistance, and methods such as hydration sealing treatment in boiling water or pressurized steam, or coating the oxide film surface with a resin have been implemented. Methods for resin coating include dissolving or dispersing the resin in an organic solvent or water and applying it by spraying, applying static electricity to the resin particles at the same time as spraying, and applying the resin electrostatically by applying an electrostatic charge to the resin particles at the same time as spraying. A method in which the object to be coated is immersed in a dispersed resin liquid and a resin film is formed using the viscosity of the resin liquid and the volatility of the solvent. A method in which a resin film is electrically formed between a counter electrode and a direct current or an alternating current, a method in which resin powder is sprayed onto a heated object, or a heated object is formed in a flowing powder. A method of forming a molten film by bringing coating materials into contact is known. The present invention provides a novel method for coating aluminum products that is fundamentally different in coating mechanism from these conventional methods.

To summarize the present invention, an aluminum product having a surface structure that is anodized and in an active state is prepared at pH 3.
．． A water-insoluble polymer coating is applied to the surface of the aluminum product by soaking it in a polymer latex containing negatively charged polymer particles without washing it with water after soaking it in an acidic solution of 0 or less. This is a method of forming layers.

Here, the surface structure in an active state refers to the surface structure that is dyed in the pore sealing test based on dyeability, and the anodized film is used in the JIS (Japanese Industrial Standards) Day 8683 dye liquid immersion bond test. A dye such as aluminum blue (Num Sengawa mBlue) in an aqueous solution of IW'V% of GenW is 2000
Refers to the surface area where even a small amount of the anodic oxide film is dyed blue after soaking in water for 15 minutes and washing with water.

In the present invention, the means for forming a polymer coating layer is similar to the conventional immersion groove coating method in its operation, but the formation mechanism of the polymer coating layer is completely different.

That is, in the conventional immersion coating method, an anodized aluminum product is immersed in a water-soluble paint and then pulled up to form a paint layer that physically adheres to the surface. If the paint layer is washed with water immediately after it is formed, most of the paint layer will be redispersed in water and no paint film will be formed.

In contrast, the method of the present invention prepares an anodized aluminum product with an active surface structure at a pH of 3.
0 or less to dissolve the aluminum oxide so that aluminum ions are present on the surface of the oxide film, and then immerse it in a polymer latex containing negatively charged polymer particles to dissolve the aluminum oxide. The ionic attraction between the aluminum ions on the surface of the oxide film and the negatively charged polymer particles causes the polymer particles to precipitate on the surface of the oxide film, and the ionic bonding force causes water to firmly adhere to the surface of the oxide film. This method forms an insoluble polymer coating layer.

Furthermore, in order to obtain a thick and uniform coating film with the immersion coating method, it is necessary to take into account the control of the viscosity, solid content, and specific gravity of the coating material, as well as the rate at which the coating material is pulled up and the setting after coating.

In this way, it is necessary to prepare a paint that is suitable for immersion painting, and in particular, when applying immersion coating to anodized aluminum products, water-soluble resin paints (
Viscosity 27±&ps, solid content 20~35%, PH8.0~
8.7, specific gravity 0.955-0.975) are used. Furthermore, polymer latex generally has a very low viscosity and was understood to be unsuitable as a coating material for dip coating, which uses the viscosity of the coating material to form a coating film. The method of the present invention uses this polymer latex, but
There is also the advantage that a highly concentrated water-insoluble resin layer can be formed even from latex with a low solids content (1%). As described above, although the operating method of immersing the object to be coated in the paint bath is the same, the present invention improves the physical adhesion in the coating film formation mechanism that utilizes the bond between aluminum ions and polymer particles. This method is completely different from the conventional dip coating method used.

Moreover, the method of the present invention is different from methods that use electricity such as the Kame-dori coating method, and simply by dipping, the method forms a dense and highly concentrated resin layer that firmly adheres to the surface of the object to be coated. This is the most distinctive feature of this method.

By the way, it is known that polymer particles generally aggregate when they come into contact with strong acidic substances.

However, the method of the present invention is different from the method of forming a coating film using such aggregation. This means that, for example, pH
Even if an anodized aluminum product that has been previously immersed in an acidic solution is immersed in a polymer latex that does not cause agglomeration even when added to a moderately acidic solution, a uniform water-insoluble polymer will remain on the surface. This is evidenced by the fact that a coalescing coating layer is formed. In other words, the method of the present invention does not simply utilize the aggregation of polymer particles caused by acid to deposit a coating film, but as described above, aluminum ions on the surface of the oxide film and negatively charged polymer particles form ionic bonds. This method utilizes a mechanism in which polymer particles are precipitated by binding to polymer particles. To explain the method of the present invention in more detail, an aluminum product is first subjected to an anodizing treatment.

Electrolytes used for anodizing include sulfuric acid, chromic acid, boric acid, phosphoric acid, pyrophosphoric acid, molybdic acid, oxalic acid, sulfamic acid, sulfosalicylic acid, sulfosuccinic acid, malonic acid, tartaric acid, citric acid, etc. Use a mixture. There are no particular restrictions on the thickness of the anodic oxide film, but
If it is less than 1, it is not practical as an oxide film, while if it is more than 35, it is unnecessary, and usually from 1 to 35, preferably from 3 to 35.
It is about 20 Buddhas. It goes without saying that the surface of an aluminum product that has been subjected to a normal anodizing treatment is dyed by the above-mentioned stainability test, but the aluminum product according to the present invention is not limited to this. Depending on the case, it may be treated with boiling water, pressurized steam, an aqueous metal salt solution, or the like. Although the method of the present invention does not interfere with such post-anodization treatment, it is necessary to have an active state, and it is necessary to have an anodized film with a surface structure that is dyed in a sealing test based on dyeability. set to target. This is because if a sealing treatment such as boiling water, pressurized steam, or metal salt treatment is applied for a long time after anodizing treatment, the activity of the anodic oxide film will be impaired, so the method of the present invention is not effective. This is because it became clear that

In addition, we can dye aluminum products that have undergone anodizing treatment.
Items colored with coloring agents such as pigments and polymer dyes, or items colored by dipping or electrolyzing in a metal salt aqueous solution,
Other materials that have a pattern such as a wood grain pattern formed on their surface are also applicable to the method of the present invention as long as they can be dyed in the above-mentioned dyeability-based pore-sealing test.

The pH of the acidic liquid was adjusted to 3.0 or less using an inorganic acid such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, or chromic acid or an organic acid such as acetic acid, formic acid, oxalic acid, or paratoluenesulfonic acid as a brewing ingredient. Use a solution.

In this case, the medium need not be water. In the present invention, the aluminum product with the surface structure in the active state is immersed in the acidic solution, and the treatment time is at least 1 minute, and in order to obtain a uniform coating thickness, it is about 5 to 10 minutes. It is preferable to immerse the bond to a certain extent.

The treatment with an acidic solution of the present invention is not limited to the above-mentioned method. Immediately after anodizing, the aluminum product is directly immersed in the acidic solution without removing the electrolyte adhering to it by washing with water. It is also possible to do so. In the method of the present invention, an aluminum product that has been anodized as described above and has a surface structure that is dyed in a sealing test based on dyeability is immersed in an acidic solution with a pH of 3.0 or less, and then a polymer latex This is a coating method in which a water-insoluble resin film is formed on the surface of the aluminum product by soaking it in water, but it is necessary to use a polymer latex whose surface is negatively charged.

This means that for polymer latex in which the polymer particles are not negatively charged, anodized aluminum products with a surface structure that is dyed in a sealing test based on dyeability are coated with a pH of 3.0 or less. This is because no water-insoluble resin layer is formed even after being immersed in an oxidizing solution and then crushed. The polymer latex used in the present invention is
Obtained by emulsion polymerization of one or more monomers having an ethylenically unsaturated double bond, or by emulsion polymerization of monomers mixed with a crosslinking agent so as to be negatively charged. It is something.

Monomers with ethylenically unsaturated double bonds include acids such as acrylic acid, methacrylic acid, itaconic acid, and maleic acid, alkyl acrylates, alkyl methacrylates, hydroxyalkyl acrylates, hydroxyalkyl methacrylates, acrylamides, and methacrylates. amides and their N-methylolated products or N-alkoxymethylolated products, acrylic or methacrylic monomers such as acrylonitrile and methacrinitrile, styrene,
It includes styrene monomers such as P-chlorostyrene and Q-methylstyrene, vinyl monomers such as vinyl acetate and vinyl propionate, and gen monomers such as butadiene, isoprene, and chloroprene. Also, monomers with phosphate stalks and ethylenically unsaturated double bonds, such as mono(2-hydroxyethyl acrylate) acid phosphate, mono(2-hydroxyethyl methacrylate) acid phosphate, mono(2-hydroxyethyl acrylate) acid phosphate, Hydroxypropyl acrylate) acid phosphate, mono(2-hydroxypropyl methacrylate) acid phosphate, mono(
3-hydroxypropyl acrylate) acid phosphate, mono(3-hydroxypropyl methacrylate)
Primary phosphate esters of acrylates or methacrylates containing hydroxyl groups such as acid phosphates, allyl alcohol acid phosphates, vinyl phosphonic acids, paravinylbenzene phosphonic acids, sulfonic acid groups and ethylenically unsaturated double monomer with a bond,
For example, sulfomethyl acrylate, 2-sulfoethyl acrylate, 2-sulfof. lopylacrylate, 3
-sulfopropyl acrylate, sulfomethyl methacrylate, 2-sulfoethyl methacrylate, 2-sulfopropyl methacrylate, 3-sulfopropyl methacrylate, styrenesulfonic acid, vinylsulfonic acid, allylsulfonic acid, and the like can also be used. Examples of crosslinking agents include thermosetting epoxy compounds, amino compounds, blocked polyisocyanate compounds, and phenol compounds.

In order to obtain an anionic polymer latex with negatively charged polymer particles, anionic polymerization initiators and/or emulsifiers are used.

Alternatively, a monomer having a functional group that causes the polymer latex to be negatively charged may be used. In the present invention, the types and amounts of these particles are not particularly limited, as long as polymer latex particles that are negatively charged as a whole can be obtained.

For example, even if an initiator such as 4,4'-azobisisobutyramidinium hydrochloride is used, anionic emulsifiers such as sodium lauryl sulfate may be used to negatively charge the entire particle. For example, it can be used in the method of the present invention. Therefore, the polymerization method for the polymer latex used in the present invention includes radical emulsion polymerization using a nonionic surfactant or anionic surfactant as an emulsifier and potassium persulfate, ammonium persulfate, etc. as an initiator, hydrogen peroxide, etc. and Fe”
Emulsion polymerization using a redox initiator, etc. can be used.

Further, emulsion polymerization without using an emulsifier, emulsion suspension polymerization using azobisisoputilonitrile, penzoyl peroxide, etc. can also be used. Examples of nonionic surfactants include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene nonylphenol ether, sorbitan monolauryl ester, sorbitan dioleyl ester, and polyoxyethylene sorbitan monostearyl ester. ,
Examples of anionic surfactants include oleic acid sodium salt, lauryl alcohol sulfate sodium salt, stearyl alcohol sulfate trietanoamine salt, dodecylbenzenesulfonic acid sodium salt,
Examples include octylnaphthalene sulfonic acid potassium salt, dioctyl sulfosuccinic acid sodium salt, polyoxylauryl sulfate ester sodium salt, polyoxyethylene nonylphenol sulfate ester potassium salt. If it is necessary to adjust the pH of the polymer latex, it may be done by adding key acids such as sulfuric acid, hydrochloric acid, nitric acid, or organic acids such as acetic acid or oxalic acid.

The resin concentration of the polymer latex used in the present invention is 0.5
~60% by weight (resin solid content) is appropriate; if it is less than 0.5% by weight, the formed water-infusible resin layer will be thin and the adhesion to the object to be coated will be poor; If it is more than that, the viscosity becomes high and it becomes difficult to obtain a stable polymer latex, which is not preferable.

Considering economic efficiency from the resin film thickness and precipitation rate, 1 to 4% by weight is preferable. The immersion time for forming a water-insoluble resin layer by immersing an anodized aluminum product with a surface structure in an active state in polymer latex varies depending on the desired resin film thickness. Formation is already visible with a soaking time of 1 min., and 3M sand to 10 min. is usually adequate. The aluminum product lifted from the polymer latex is further soaked in water to remove excess polymer latex, if necessary, and then dried.
Drying is usually carried out at room temperature to 20,000 ℃ for 5 to 30 minutes. When unsaturated monomers are polymerized or a crosslinking agent such as a thermosetting epoxy compound, an amino compound, a block polyisocyanate compound, or a phenol compound is included,
It is necessary to use heating temperatures and times necessary for the curing reaction. The aluminum products targeted by the present invention include plates, rods, wires, and other molded products with complex shapes, and are not limited in shape or size.

Furthermore, when processing a long frame such as an aluminum sash, either horizontal or vertical hanging methods can be adopted. Next, "Examples will be shown in order to explain the present invention more specifically.

Note that all parts in the following examples are parts by weight.
Preparation of Latex A: 1 liter of deionized water in a four-wall flask equipped with a thermometer, reflux condenser, dropping funnel and nitrogen gas inlet tube.
5 parts of sodium lauryl sulfate, 0.1 part of sodium lauryl sulfate, and 0.5 part of potassium persulfate were added, and the mixture was heated to 80 qo while stirring.

Add to this 5 groups of ethyl acrylate, 5 groups of methyl methacrylate.
The mixed solution of Ikarito was added dropwise from the dropping funnel over a period of 2 hours.
After the dropwise addition was completed, the reaction was continued for another 4 hours to prepare an acidic and stable latex with a conversion rate of 95% or more. This latex was diluted to a solid content of 2% by weight, and the pH was measured to be 2.5. Preparation of Latex B Add 0.02N ammonium hydroxide aqueous solution to Latex A to adjust the pH to 4.0.
Adjusted to.

Preparation of test materials JISA5052 pretreated by conventional method
An aluminum plate (200 ribs x 6.5 sides x 0.5 sides) was used as an anode and carbon was used as a cathode.
qo, IA/d, electricity was applied to each of the three powders, each powder was washed with tap water, and then immersed in L8000 warm water for 5 minutes to prepare a sample. Examples 1-8 and Comparative Examples 1-8 Test material A
After soaking in a hydrochloric acid aqueous solution having a pH of 2.0 for 5 minutes, latexes A and B' were coated at room temperature for different soaking times.

Claims (1)

[Claims] 1. An aluminum product that has been anodized and has a surface structure in an active state is immersed in an acidic solution with a pH of 3.0 or less, and then immersed in a negatively charged heavy metal product without washing with water. A method for coating an aluminum product, which comprises immersing the aluminum product in a polymer latex having coalesced particles to form a water-insoluble polymer coating layer on the surface of the aluminum product. 2. The coating method according to claim 1, wherein the acidic liquid has a pH adjusted to 3.0 or less by dissolving at least one type of organic acid or inorganic acid.